A semiconductor device, one or more of which are included in an integrated circuit (IC), includes a number of electronic devices. One way in which to represent a semiconductor device is with a plan view diagram referred to as a layout diagram (hereinafter, layout). A layout is hierarchical and is decomposed into modules which carry out higher-level functions as required by the semiconductor device's design specifications. In some circumstances, a semi-custom design (SCD) project decomposes the modules into macro cells, standard cells and custom cells.
For a given SCD project, a custom cell is designed with an arrangement that is specific to the given SCD project in order to provide (in operation) a higher-level logic function that is specific to the SCD project. By contrast, a library of standard cells is designed with no particular project in mind and includes standard cells which provide (in operation) common, lower-level logic functions. In terms of a footprint within a layout (from the perspective of a plan view), custom cells are larger (typically much larger) than standard cells. Moreover, for a given library, all of the standard cells have at least one dimension which is the same size (typically, the size being a multiple of a library-specific fixed dimension) in order to facilitate placement of the standard cells into a layout. Typically, the direction of the fixed dimension is parallel to the vertical direction or Y-axis such that the fixed dimension is referred to as the height of the standard cell. As such, standard cells are described as being predefined with respect to a given SCD project. Custom cells may or may not have at least one dimension that is the same size as the corresponding dimension of the standard cells.
As technology improves, the density of a semiconductor device (in terms of the number of electronic devices per unit area or per unit volume) increases. One way in which to increase semiconductor device density is to reduce the size of the fixed dimension of all standard cells in a given library.